The development of energy storage is necessary in order to reduce our dependency on fossil fuels and to improve our ability to store energy produced by energy sources where the energy output is controlled by weather rather than energy needs. Energy sources such as wind and wave may produce an excess of energy when the demand for energy is low, such as during the night, and the ability to efficiently store the excess energy until the demand increases is required.
There are several types of energy storage currently used, the type used depends upon the quantities of energy storage required as some energy storage types become astronomically expensive or unachievably large. Conventional compressed air energy storage (CAES) is useful for large scale energy storage such as grid scale, from around ten to 300 megawatts. In principle, a CAES system in combination with a wind farm connected to the grid, for example, is able to store energy underground by compressing air and storing the compressed air in an impermeable cave when the energy produced by the wind farm is not required by the demands on the grid. When energy demands increase, the compressed air in the cave is released and is used to produce electricity. Because conventional CAES systems require specific geological conditions, the location of CAES sites is limited.
WO2010138677 discloses an adsorption enhanced compressed air energy system whereby the storage vessels are provided with porous materials such as carbon, silica gel or zeolites. The compressed fluid are more easily stored in the presence of the porous material because the absorbed phase is much denser than the free fluid, thus reducing the volume of the storage tank required.